Conventionally, a motor has been known which includes a rotor and a stator in a cylindrical tube shape which is disposed on an outer peripheral side of the rotor (see, for example, Japanese Patent Laid-Open No. 2010-57211). In the motor described in the Patent Literature, a stator includes a stator core and a drive coil which is wound around a teeth part of a stator core through an insulator. The stator core is formed by combining a plurality of split cores which are divided in a circumferential direction of the stator. The split core is provided with an outer side yoke part connected with an outer side end of a tooth part in a radial direction of the stator. Further, the Patent Literature describes that the stator core may also utilize a so-called curling core which is structured so that a belt-shaped core in which outer side yoke parts are connected with each other is bent in a circular ring shape and its end parts are connected with each other.
The curling core is, for example, as shown in FIG. 7, formed by using an original core body 105 provided with a belt-shaped portion 103 in a straight line shape, which is structured of a plurality of outer side yoke parts 102 connected with each other through connecting parts 101, and teeth parts (salient pole parts) 104 which are protruded in a direction perpendicular to a longitudinal direction of the belt-shaped portion 103 from each of the plurality of the outer side yoke parts 102. Further, the curling core is structured by successively bending the belt-shaped portion 103 at the connecting parts 101, for example, in the order shown in FIGS. 8A through 8C and by connecting both ends of the belt-shaped portion 103 with each other so that the belt-shaped portion 103 is set in a circular ring shape and that the salient pole parts 104 are protruded to an inner side in a radial direction.
In the motor described in the Patent Literature, a tip end face of the salient pole part 104 (inner side face in a radial direction of the stator) is formed in a curved face shape which is a circular arc shape when viewed in an axial direction of the stator. The tip end faces of the salient pole parts 104 are disposed in a design on an imaginary circle “VC10” with the axial center “C10” of the stator as a center when viewed in the axial direction of the stator so that air gaps (gap space in a radial direction between a rotor and the stator) are constant in a circumferential direction of the stator.
In a case that the belt-shaped portion 103 is successively bent in the order shown in FIGS. 8A through 8C, the connecting part 101 which is first bent from a state shown in FIG. 7 to a state shown in FIG. 8A is also acted with a force in a bending direction when the belt-shaped portion 103 is secondly bent from the state shown in FIG. 8A to a state shown in FIG. 8B and, even when the belt-shaped portion 103 is thirdly bent from the state shown in FIG. 8B to a state shown in FIG. 8C. In other words, a force in a bending direction is acted two times on the first bent connecting part 101 after having been bent.
Further, the connecting parts 101 which are secondly bent are also acted with a force in a bending direction when the belt-shaped portion 103 is thirdly bent from the state shown in FIG. 8B to the state shown in FIG. 8C. In other words, a force in a bending direction is acted once on the second bent connecting parts 101 after having been bent. On the other hand, the connecting parts 101 which are bent thirdly are not acted with a force in a bending direction after having been bent.
According to examinations of the present inventors, the present inventors have found that, for example, in a case that the number of the salient pole parts 104 is small like a case that the number of the salient pole parts 104 is six, when the belt-shaped portion 103 is successively bent as shown in FIGS. 8A through 8C, tip end faces of the salient pole parts 104A connected with two outer side yoke parts 102A disposed at both ends of the belt-shaped portion 103 in the original core body 105 are largely displaced from the imaginary circle “VC10” when viewed in the axial direction of the stator.
In other words, the present inventors have found that, in a case that the number of the salient pole parts 104 is small, when the belt-shaped portion 103 is successively bent as shown n FIGS. 8A through 8C, the circularity of a circle formed by the tip end faces of six salient pole parts 104 is deteriorated by the salient pole parts 104A when viewed in the axial direction of the stator. Specifically, the present inventors have found that, as shown in FIG. 9 which is an enlarged view of the “G” part in FIG. 8C, when viewed in the axial direction of the stator, the tip end faces of the salient pole parts 104A are largely displaced to an outer side in the radial direction from the imaginary circle “VC10” and the circularity of a circle formed by the tip end faces of six salient pole parts 104 is deteriorated by the salient pole parts 104A.